I haven't found a whole lot on Merritt Griswold. He was born in New York (probably Brooklyn) around 1835 to William and Zilpha Griswold. His mother (whose maiden name was Busch) had family in Missouri which is probably how Griswold ended up in St. Louis for a few years.
He served as a Captain with the 3rd regiment of the United States Reserve Corp during the Civil War. Interestingly, military records show him mustering in on May 8, 1861 in St. Louis and then mustering out on August 17, 1861. So it looks like Griswold, who would have been in his mid 20's when the war started, was not a member of the active military during the war. I guess his unit never got called up.
It appears that Griswold was a mechanical engineer by trade. After the war, he was working for the Knox Railway Clamp Company and, in the 1880 census, he listed his occupation as "pump maker". Griswold also holds two patents. One is for a "ventilating apparatus", which from what I can understand is some kind of flue, and another for a type of window glass.
Griswold lived most of his adult life in Englewood, New Jersey. He was married to a woman named Emma and had three daughters (Grace, Edith, and Carolyn). He died on march 24, 1915 and is buried in Woodlawn Cemetery in the Bronx.
I can't find any connection between Griswold and baseball after he left St. Louis.